1. Field of the Invention
This invention relates to cargo carrying containers, as used in over-the-road applications and, more particularly, to a cargo carrying container with a peripheral wall structure which extends around a cargo storage space and incorporates at least one reinforcing corrugated sheet.
2. Background Art
Myriad designs have been developed for the peripheral wall structures of cargo carrying containers, as used in single mode and multi-modal applications. Designers of these types of containers focus principally on two broad objectives. One of these objectives is to optimize the cargo space within the maximum permitted external dimensions of such containers that are permitted by the governmental agencies that regulate the trucking industry. The other objective is to produce a peripheral wall structure that will withstand vertical, transverse and lateral loading forces encountered during the normal use and operation of vehicles incorporating the cargo containers.
One common cargo container construction has front, rear, and side walls formed between upper and lower rail assemblies to cooperatively produce a cubical cargo space of desired dimensions. The upper and lower rail assemblies are respectively integrated into roof and peripheral wall assemblies and resist forces tending to bend the cargo container from its squared shape.
By reason of its weight, the roof assembly imparts a significant vertical force upon the peripheral wall structure. In a tractor/semitrailer combination, vertical loading is additionally imparted at discrete locations through a) a wheel carriage adjacent the rear of the cargo container, b) a coupler assembly at the front of the cargo container, and c) a landing gear aft of the coupler assembly that maintains a desired orientation of the cargo container relative to a support surface with the cargo container separated from a towing vehicle/tractor. Somewhat different vertical loading forces are encountered with the cargo container and towing vehicle therefor permanently integrated.
Non-vertical loading forces are imparted to the peripheral wall structure by wind, cargo shifting, and bending/distortion forces as the cargo container is transported, as through its dedicated towing vehicle in over-the-road use, or with the cargo container on rails or upon a vessel in water with multi-modal configurations. Still further, the non-vertical forces are affected by the manner in which the cargo is distributed within the storage space and secured to the peripheral wall structure to control shifting thereof.
Heretofore, it has been common to form particularly the side walls of the cargo container with vertically extending, elongate stiffeners/side posts. The stiffeners/side posts are generally made from formed steel, or other material as requirements allow or dictate, with each stiffener/side post having a generally U-shaped cross-sectional configuration, with a base, spaced parallel legs, and outturned flanges associated one each with the legs. The flanges have co-planar surfaces which are abuttable to exposed external panels which can be secured to the stiffeners/side posts, as by adhesive or mechanical fasteners. The external panels provide strength and a moisture barrier with a smooth, continuous extent that is aesthetically desirable and lends itself to the application of signage or other aesthetic or informational additions. Internal panels may optionally be attached to the stiffeners/side posts.
The stiffener/side post composition, shape, dimensions, and spacing will dictate the strength of the side walls. The depth of the stiffeners/side posts also determines in good part the degree of rigidity and ability to resist deflection under loading. Generally, the deeper the stiffeners/side posts, i.e. the longer the length of the legs, the more resistant the stiffeners/side posts are to bending. However, by increasing the depth of the stiffeners/side posts, the cargo space is correspondingly reduced. In the case of the side walls, this reduced dimension is doubled by reason of the inclusion of stiffeners/side posts at each side wall.
The stiffeners/side posts in a columnar or compressive manner absorb the vertical loads imposed on the side walls. It is sometimes necessary to add extra stiffeners/side posts in the vicinity of the wheeled carriage, the coupler assembly, and the landing gear to prevent the stiffeners/side posts from buckling in compression. Further, with a multi-modal configuration, the cargo carrying container must be loaded onto and unloaded from a rail car or ocean going vessel by means of a handling device that lifts, through normally four spaced lifting pads, which are usually 4 inches in width, by 18 inches in length. Lifting forces imparted through these pads can also create stiffener/side post failures. Thus additional stiffeners/side posts, or stiffeners/side posts of different strengths, may need to be added strategically to the side walls to handle these loads. The forces imparted at the lift areas may also vary depending upon the weight and load distribution of the cargo. This may require an increased number of stiffeners/side posts or a heavier construction for some or all of the stiffeners/side posts. Aside from detrimentally affecting the size of the cargo storage space, the heavier stiffeners/side posts represent an added expense and may also add significantly to the overall weight of the cargo carrying container. By reducing the spacing between the stiffeners/side posts, the material and labor costs associated with manufacture correspondingly increase.
Generally, designers of cargo carrying containers are forced to balance the often competing objectives of a) enhancing the integrity of the peripheral wall structure bounding the cargo space, b) reducing the overall depth of stiffeners/side posts to maximize storage volume, c) maintaining the weight of the cargo container within a certain range, and d) controlling the cost of manufacturing the cargo container.
With this conventional stiffener/side post construction, exposed internal panels may be attached, either by the use of adhesive or mechanical fasteners, or by press fitting the same in place, as disclosed in U.S. Pat. No. 6,607,237. In one form, the stiffeners/side posts are configured in cross section to define an outwardly offset edge which supports the thickness of the internal panels without causing a projection of the internal panels inwardly to beyond the base portion of the side posts. The internal panels ideally cooperatively produce a continuous flat surface, in conjunction with the side posts, to facilitate sliding of cargo against and along the walls, during loading and unloading, without hang up.
It is also known to use corrugated sheets adjacent to the bottom of the wall panels on the inside of the cargo container as scuff panels that resist damaging impacts to the stiffeners/side posts that may be imparted through loading equipment such as fork lift trucks, and also guide sliding movement of cargo thereagainst. By doing so, the dimensions of the cargo space are further reduced by the thickness of the corrugated sheets at each wall at which they are used.
It is also known to use corrugated welded steel to form exposed portions of peripheral wall structures on cargo carrying containers. This is a common construction in the ocean going trade that has resulted from decades of testing different designs, through experience in handling and through cost reduction programs. These containers are generally standardized in size and design as required for economical handling and international transportation. By using corrugated sheets, a relatively low cost container can be constructed with continuous walls which have high strength for both vertical and non-vertical loading, and which generally can be made watertight for protection of cargo on the open seas.
While this type of container has a number of advantages, both from economic and functional standpoints, there are a number of drawbacks inherent in this design. First of all, the exposed corrugated sheet material accounts for poor aerodynamic characteristics. The corrugated, exposed surface creates a significant amount of wind drag which, in an over-the-road application, may reduce fuel efficiency for the towing vehicle.
Additionally, the corrugated panels are generally unattractive and may become even more so after use. As the panels become scratched or scored in normal use, the material tends to corrode, which condition worsens over time.
Additionally, the irregular, exposed surface of the corrugated sheets does not lend itself to the application of any identifying or informational material that the user may desire.